Valganciclovir hydrochloride is chemically, L-valine, 2-[(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)-methoxy]-3-hydroxypropanyl ester, monohydrochloride, having the structure as represented by Formula I.

It is the hydrochloride salt of mono-L-valyl ester prodrug of antiviral compound ganciclovir of Formula II.

Valganciclovir hydrochloride is marketed in the United States under the brand name Valcyte® for the treatment of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome and for the prevention of cytomegalovirus disease in kidney, heart, and kidney-pancreas transplant patients at high risk.
Several methods for the preparation of valganciclovir hydrochloride are reported in literature such as those described in U.S. Pat. Nos. 6,083,953; 6,340,756; and WO 2005/092891, which are incorporated herein by reference.
The processes described in the literature involve preparation of valganciclovir by the deprotection of mono-benzyloxycarbonyl-L-valine ganciclovir of Formula III
in methanol or ethanol.
The present inventors have observed that when deprotection of mono-benzyloxycarbonyl-L-valine ganciclovir of Formula III is carried out using methanol or ethanol, N-methyl valganciclovir and N-ethyl valganciclovir impurities are formed along with valganciclovir hydrochloride. United States Pharmacopoeia (USP) for valganciclovir hydrochloride requires N-methyl valganciclovir impurity to be controlled within a limit of not more than 0.3% in valganciclovir hydrochloride.